diff --git a/crypto/cipher/e_aes.c b/crypto/cipher/e_aes.c
index 6e4b7a08..99883450 100644
--- a/crypto/cipher/e_aes.c
+++ b/crypto/cipher/e_aes.c
@@ -283,7 +283,8 @@ void aesni_ctr32_encrypt_blocks(const uint8_t *in, uint8_t *out, size_t blocks,
 #endif
 
 static int aes_init_key(EVP_CIPHER_CTX *ctx, const uint8_t *key,
-                        const uint8_t *iv, int enc) {
+                        const uint8_t *iv, int enc)
+                        OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS {
   int ret, mode;
   EVP_AES_KEY *dat = (EVP_AES_KEY *)ctx->cipher_data;
 
@@ -404,7 +405,8 @@ static char aesni_capable(void);
 
 static ctr128_f aes_ctr_set_key(AES_KEY *aes_key, GCM128_CONTEXT *gcm_ctx,
                                 block128_f *out_block, const uint8_t *key,
-                                size_t key_len) {
+                                size_t key_len)
+                                OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS {
   if (aesni_capable()) {
     aesni_set_encrypt_key(key, key_len * 8, aes_key);
     if (gcm_ctx != NULL) {
diff --git a/crypto/internal.h b/crypto/internal.h
index 30e6e924..38f9820e 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -120,6 +120,26 @@ extern "C" {
 #endif
 
 
+/* MSVC will sometimes correctly detect unreachable code and issue a warning,
+ * which breaks the build since we treat errors as warnings, in some rare cases
+ * where we want to allow the dead code to continue to exist. In these
+ * situations, annotate the function containing the unreachable code with
+ * OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS after its parameters:
+ *
+ *    void f() OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS {
+ *       ...
+ *    }
+ *
+ * Note that MSVC's reachability analysis seems to operate on a whole-function
+ * basis, so the annotation must be placed on the entire function, not just a
+ * block within the function. */
+#if defined(_MSC_VER)
+#define OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS \
+        __pragma(warning(suppress:4702))
+#else
+#define OPENSSL_SUPPRESS_UNREACHABLE_CODE_WARNINGS
+#endif
+
 /* st_CRYPTO_EX_DATA_IMPL contains an ex_data implementation. See the comments
  * in ex_data.h for details of the behaviour of each of the functions. */
 struct st_CRYPTO_EX_DATA_IMPL {